Science Express
Chinese Astronomers Discover One of the Universe's Oldest Stars - A Stellar Relic 260 Times Heavier Than the Sun
They found one of the oldest stars ever seen, which has been around for almost the entire history of the universe.

Editor’s Note:
This finding sheds light on the early days of the universe when the first stars were being born and shaping the cosmos. It's incredible to think that this star has been around for almost the entire history of the universe. It's a stellar relic and an epic cosmological mystery that scientists are now closer to solving.

A team of astronomers from the National Astronomical Observatories of the Chinese Academy of Sciences has identified a star in the Milky Way that has a very unusual chemical composition, suggesting that it was formed from the debris of a massive explosion in the early universe. The star, named LAMOST J1010+2358, is located in the halo of our galaxy and has very low levels of sodium and cobalt, as well as a large difference between the abundances of odd and even charge number elements. These features match the predictions of a theoretical model of a pair-instability supernova (PISN), which is a type of explosion that occurs when the core of a very massive star collapses due to the creation of electron-positron pairs. The researchers estimate that the progenitor star of the PISN had a mass of 260 times that of the sun, making it one of the first and most massive stars in the universe. The discovery of LAMOST J1010+2358 is the first direct evidence for the existence of such very massive stars and PISNe in the early universe, shedding light on the formation and evolution of the first stars and galaxies. The study was published in the journal Nature on June 7, 2023.

The first stars were born around 100 million to 250 million years after the Big Bang, which occurred about 13.8 billion years ago. But scientists are still in the dark about how the mass of this first generation of stars was distributed. Modeling of stars in the early universe indicates that some of these stellar bodies may have had masses equivalent to hundreds of suns. Massive stars end their lives with gigantic cosmic explosions called supernovae, but stars with masses between 140 and 260 times that of the sun back then would have ended their lives in supernova blasts different from those typically seen in the later universe (known as Type II and Type Ia supernovae), study team members said. These unique explosions are referred to as pair-instability supernovae (PISNe).

Pair-instability supernovae are different from ordinary supernovae that occur in less massive stars and leave behind neutron stars or black holes. Pair-instability supernovae also produce a unique chemical signature in the next generation of stars, because they synthesize and eject different elements than ordinary supernovae. Pair-instability supernovae are predicted to occur in the early universe when the first stars were very massive and had low metallicity (low abundance of elements other than hydrogen and helium). These first stars are also called Population III stars, and they are thought to have formed the first galaxies and influenced cosmic reionization. However, until now, no clear evidence for pair-instability supernovae from the first stars has been found.

The researchers utilized data gathered by the Chinese Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in Hebei province, combined with follow-up observations from the Subaru Telescope in Hawaii, determining that LAMOST J1010+2358 originated from a gas cloud dominated by remnants of a star up to 260 times more massive than the Sun that died in an extreme supernova explosion. The most significant chemical evidence marshaled by the team was an extremely low abundance of sodium and cobalt and a large variance between elements that have odd and even numbers of electrons. This is significant because PISNe occurs due to an instability caused by the production of electron and anti-electron — or positron — pairs. This instability reduces thermal pressure inside the core of a very massive star and leads to a partial collapse and then a runaway thermonuclear explosion.

The discovery of LAMOST J1010+2358 is a breakthrough in understanding the nature and fate of the first stars in the universe, as well as their impact on subsequent generations of stars and galaxies. The researchers hope to find more stars with similar chemical signatures in future surveys, which could help them constrain the mass distribution and frequency of PISNe from Population III stars.